Sulfydryl-modified potato porous esterified starch as well as preparation method and application thereof

Abstract

The invention discloses sulfydryl-modified potato porous esterified starch and a preparation method and application thereof.The method comprises the steps that 1, potato starch and a sulfuric acid solution with the concentration being 0.5 mol / L to 1.5 mol / L are mixed according to the mass ratio of 1: (90-95), heating and stirring are conducted for 8 min to 10 min under the water bath condition of 60 DEG C to 70 DEG C, then ultrasonic dispersion is conducted, after cooling is conducted, sediment is separated out through centrifugation, freeze drying is conducted, and the sulfydryl-modified potato porous esterified starch is obtained; potato porous starch is obtained; 2, firstly adding potato porous starch into deionized water to prepare starch milk with the mass fraction of 20%-50%, adjusting the pH value of the starch milk to be alkaline, then adding a sulfhydryl compound into the starch milk according to the mass ratio of the sulfhydryl compound to the potato porous starch of (1-1.5): 1, stirring for 3-8 hours at the temperature of 30-50 DEG C to obtain esterified starch milk, adjusting the pH value of the esterified starch milk to be neutral, and stirring for 2-3 hours at the temperature of 30-50 DEG C to obtain esterified starch; and then centrifugally separating out a precipitate, and freeze-drying to obtain the sulfydryl-modified potato porous esterified starch which has relatively high water absorption and oil absorption and good heavy metal adsorption performance.

Description

Technical Field

[0001] The invention belongs to the technical field of starch processing, and relates to a thiol-modified potato porous esterified starch, a preparation method and an application thereof. Background Art

[0002] Porous starch, also known as microporous starch, is a new type of modified starch with small pores on the surface. It can be used as an organic adsorbent, microcapsule and embedding material, and is widely used in the fields of medicine, pesticides, printing, daily chemicals, cosmetics and food. Compared with natural starch, porous starch has a larger specific surface area and specific pore volume, good water absorption and oil absorption performance, low cost, non-toxicity and natural degradation. It has been widely studied. The existing porous starch preparation method generally uses specific enzymes, such as glucoamylase or α-amylase, to hydrolyze starch to form a porous structure. However, the acquisition steps of this biological enzyme are complicated and costly, and its activity is easily affected by storage conditions.

[0003] Esterified starch is an important starch derivative, which is the product of starch modified by esterification. It has many unique advantages, such as thermoplasticity, film-forming property, hydrophobicity and thermal stability. It has unique advantages and application potential in fine chemical manufacturing such as food industry, papermaking industry, and pharmaceutical processing field. The common esterified starch on the market is often used as an active packaging material for packaging drugs, flavors and vitamins, or as an intermediate for synthesizing organic compounds, or as an adsorbent to remove heavy metal ions in wastewater. However, the existing esterified starch generally has the problem of low lipophilicity, which generally does not exceed 60%, resulting in low adsorption efficiency during actual application and a large amount of adsorbent used in actual use; in addition, the modified groups of some esterified starches have a strong ability to bind water, and form a high-viscosity complex when in contact with water, thereby losing their original particle structure and functional properties.

[0004] Therefore, it is expected that different functional groups can be grafted onto the surface of porous starch through esterification reaction, thereby preparing porous esterified starch with different functions or uses. Summary of the invention

[0005] The present invention aims to provide a thiol-modified porous esterified potato starch and a preparation method and application thereof. Not only is the preparation method simple, but the prepared porous esterified potato starch has high water and oil absorption and good heavy metal adsorption performance.

[0006] The present invention is achieved through the following technical solutions:

[0007] A method for preparing thiol-modified porous esterified potato starch comprises the following steps:

[0008] Step 1: Mix potato starch and sulfuric acid solution with a concentration of 0.5 - 1.5 mol / L according to a mass ratio of 1:(90 - 95). Under the water bath condition of 60 - 70 °C, heat and stir for 8 - 10 min, then perform ultrasonic dispersion. After cooling, centrifuge to separate the precipitate, and freeze-dry to obtain porous potato starch.

[0009] Step 2: First, add the porous potato starch into deionized water to prepare a starch milk with a mass fraction of 20% - 30%. Adjust the pH value of the starch milk to alkaline, and then take a thiol compound and add it to the starch milk according to the mass ratio of (1 - 1.5):1 of the thiol compound to the porous potato starch. Stir at 30 - 50 °C for 3 - 8 h to obtain an esterified starch milk. Adjust the pH value of the esterified starch milk to neutral, then centrifuge to separate the precipitate, and freeze-dry to obtain thiol-modified porous potato esterified starch.

[0010] Furthermore, the average particle size of the potato starch in Step 1 is 35 μm, and the amylose content is 22%.

[0011] Furthermore, the ultrasonic dispersion in Step 1 is performed at a frequency of 100 - 150 KHz for 5 - 10 min.

[0012] Furthermore, the centrifugation in Step 1 and Step 2 is carried out at a rotation speed of 4000 - 8000 r / min for 5 - 10 min.

[0013] Furthermore, the temperature of freeze-drying in Step 1 and Step 2 is -40 °C.

[0014] Furthermore, in Step 2, a NaOH solution with a concentration of 2 mol / L is used to adjust the pH value of the starch milk to 8 - 10.

[0015] Furthermore, in Step 2, a HCl solution with a concentration of 0.5 mol / L is used to adjust the pH value of the esterified starch milk to neutral.

[0016] Furthermore, the thiol compound in Step 2 is thioglycolic acid or thiolactic acid.

[0017] A thiol-modified porous potato esterified starch has an oil absorption rate ≥ 100%, a water absorption rate ≥ 130%, and a degree of esterification DS ≥ 1.25%.

[0018] Application of a thiol-modified porous potato esterified starch as a heavy metal ion remover.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects:

[0020] First, make potato starch absorb water and swell under acidic conditions, and then use ultrasonic-assisted acid to incompletely hydrolyze the starch. When the starch shell is damaged, the internal vesicles overflow to form hollow potato porous starch. Then, use a mercapto compound to esterify and modify the starch with a hollow structure. Since starch contains a large number of hydroxyl and aldehyde groups, it can provide enough sites for the binding of mercapto compounds. The carboxyl group of the mercapto compound undergoes esterification binding with the hydroxyl and aldehyde groups on the starch, exposing the mercapto group of the mercapto compound on the surface of the porous starch. Finally, a mercapto-modified potato porous esterified starch with a mercapto group as the active group is synthesized, which has high adsorption and stability. Its oil absorption rate is ≥100%, water absorption rate is ≥130%, degree of esterification DS≥1.25%, and it can be used as an active adsorbent to remove free radicals and heavy metal ions in wastewater, and can also be used in the food and pharmaceutical fields for active packaging materials and organic compound intermediates.

[0021] The process for preparing the mercapto-modified potato porous esterified starch of the present invention is simple, does not involve biological enzymes, has a lower preparation cost, and the prepared mercapto-modified potato porous esterified starch has uniform pore sizes and strong heavy metal ion binding ability. The removal rates of lead, cadmium, chromium, and mercury ions in sewage all reach more than 83%, and it has broad application prospects. Description of the Drawings

[0022] Figure 1 SEM image of the mercapto-modified potato porous esterified starch prepared in Example 1 of the invention. Detailed Description of the Invention

[0023] The following further elaborates on the present invention with specific examples, which is an explanation rather than a limitation of the present invention.

[0024] In Examples 1 to 3 of the present invention, the average particle size of the selected potato starch is 35 μm, and the amylose content is 22%.

[0025] Example 1

[0026] Step 1: Mix potato starch and a sulfuric acid solution with a concentration of 0.5 mol / L according to a mass ratio of 1:90. Under the water bath condition of 60 °C, heat and use a magnetic stirrer to stir at a speed of 100 r / min for 10 min to prevent starch precipitation. Then, under a frequency of 100 KHz, perform ultrasonic dispersion for 10 min. After cooling to room temperature, centrifuge at a speed of 4000 r / min for 10 min to separate the precipitate, and freeze-dry at -40 °C to obtain potato porous starch;

[0027] Step 2: First, add potato porous starch into deionized water to prepare a starch milk with a mass fraction of 20%. Use a NaOH solution with a concentration of 2 mol / L to adjust the pH value of the starch milk to 8. Then, according to the mass ratio of mercaptopropionic acid to potato porous starch of 1:1, take mercaptopropionic acid and add it to the starch milk. Stir magnetically at 30 °C for 8 h to obtain an esterified starch milk. Use a HCl solution with a concentration of 0.5 mol / L to adjust the pH value of the esterified starch milk to neutral. Centrifuge at a speed of 4000 r / min for 10 min to separate the precipitate. Freeze-dry at -40 °C to obtain mercapto-modified potato porous esterified starch.

[0028] From Figure 1 It can be seen that the mercapto-modified potato porous esterified starch prepared in Example 1 maintains a relatively complete starch granule structure, with a large number of small holes distributed on its surface. Due to the existence of the porous structure, its specific surface area increases, providing more binding sites for mercapto modification. Based on the biological activity of mercapto and its strong chelating effect on heavy metal ions, the mercapto-modified potato porous esterified starch can be used in the medical field and for the removal of heavy metal ions in water.

[0029] Example 2

[0030] Step 1: Mix potato starch and a sulfuric acid solution with a concentration of 1.0 mol / L according to a mass ratio of 1:92. Heat in a water bath at 65 °C and use a magnetic stirrer to stir at a speed of 125 r / min for 9 min to prevent starch precipitation. Then, under a frequency of 125 KHz, perform ultrasonic dispersion for 7.5 min. After cooling to room temperature, centrifuge at a speed of 6000 r / min for 8 min to separate the precipitate. Freeze-dry at -40 °C to obtain potato porous starch;

[0031] Step 2: First, add potato porous starch into deionized water to prepare a starch milk with a mass fraction of 25%. Use a NaOH solution with a concentration of 2 mol / L to adjust the pH value of the starch milk to 9. Then, according to the mass ratio of mercaptopropionic acid to potato porous starch of 1.25:1, take mercaptopropionic acid and add it to the starch milk. Stir magnetically at 40 °C for 5 h to obtain an esterified starch milk. Use a HCl solution with a concentration of 0.5 mol / L to adjust the pH value of the esterified starch milk to neutral. Centrifuge at a speed of 6000 r / min for 8 min to separate the precipitate. Freeze-dry at -40 °C to obtain mercapto-modified potato porous esterified starch.

[0032] Example 3

[0033] Step 1: Mix potato starch and sulfuric acid solution with a concentration of 1.5 mol / L according to a mass ratio of 1:95. Under the water bath condition of 70 °C, heat and use a magnetic stirrer to stir at a speed of 150 r / min for 8 min to prevent starch precipitation. Then, under a frequency of 150 KHz, perform ultrasonic dispersion for 5 min. After cooling to room temperature, centrifuge at a speed of 8000 r / min for 5 min to separate the precipitate, and freeze-dry at -40 °C to obtain porous potato starch;

[0034] Step 2: First, add the porous potato starch to deionized water to prepare a starch milk with a mass fraction of 30%. Use a NaOH solution with a concentration of 2 mol / L to adjust the pH value of the starch milk to 10. Then, according to the mass ratio of mercaptopropionic acid to porous potato starch of 1.5:1, take mercaptopropionic acid and add it to the starch milk. Under the condition of 50 °C, stir magnetically for 3 h to obtain an esterified starch milk. Use a HCl solution with a concentration of 0.5 mol / L to adjust the pH value of the esterified starch milk to neutral, centrifuge at a speed of 8000 r / min for 5 min to separate the precipitate, and freeze-dry at -40 °C to obtain mercapto-modified porous potato esterified starch.

[0035] Perform performance tests on the mercapto-modified porous potato esterified starch prepared in Examples 1 to 3:

[0036] 1) Water absorption rate determination: Weigh 5 g each of the mercapto-modified porous potato esterified starch prepared in Examples 1 to 3, mix with excessive distilled water and vortex for 3 min. After standing at room temperature for 30 min, centrifuge at a speed of 5000 r / min for 10 min, suck out the supernatant, calculate the mass of the lower precipitate, thereby obtaining the water absorption mass of the sample. Calculate the water absorption rate according to the ratio of the water absorption mass to the original sample mass. The results are shown in Table 1;

[0037] 2) Oil absorption rate determination: Weigh 5 g each of the mercapto-modified porous potato esterified starch prepared in Examples 1 to 3, mix with soybean oil and vortex for 3 min. After standing at room temperature for 30 min, centrifuge at a speed of 5000 r / min for 10 min, suck out the supernatant, calculate the mass of the lower precipitate, thereby obtaining the oil absorption mass of the sample. Calculate the oil absorption rate according to the ratio of the oil absorption mass to the original sample mass. The results are shown in Table 1;

[0038] 3) Degree of esterification determination: Weigh 5 g each of the mercapto-modified porous potato esterified starch prepared in Examples 1 to 3, add 25 mL of hydrochloric acid-isopropanol solution with a concentration of 2.5 mol / L respectively, stir for 30 min, then add 50 mL of isopropanol solution with a concentration of 90%, stir for 10 min, and then filter using a sintered glass funnel (G2 model), and wash with isopropanol solution with a concentration of 90% until there is no Cl in the filtrate- Up to this point, the precipitate was centrifuged and transferred to a 250 mL conical flask. 50 mL of distilled water was added and 3 drops of 1% phenolphthalein indicator were added. It was titrated with 0.1 mol / L NaOH solution until it turned slightly pink. 25 mL of 0.5 mol / L NaOH standard solution was added. The conical flask was capped and placed in a shaker at a constant temperature of 25 °C and shaken for 30 min. Then it was titrated with 0.5 mol / L HCl standard solution until the red color disappeared. Three parallel experiments were carried out. Finally, the degree of esterification was calculated. The results are shown in Table 1;

[0039]

[0040] In the formula, 162 is the molar mass of glucose residue / (g / mol); 92 is the relative molecular mass of thioglycolic acid, and when thiolactic acid is used, it is calculated as 106; A is the volume of NaOH solution consumed in the titration / mL; M is the molar concentration of NaOH solution used in the titration / (mol / L); W is the mass of thiol-modified porous starch prepared / g;

[0041] 4) Determination of heavy metal ion removal rate: 50 mL of sewage containing lead, cadmium, chromium, and mercury ions were prepared respectively, with a total of three groups. 2.0 g of thiol-modified potato porous esterified starch prepared in Examples 1 to 3 were added respectively. It was left standing for 1 h. Inductively coupled plasma mass spectrometry was used to measure the heavy metal ion content in the sewage before and after adding the thiol-modified potato porous esterified starch, and the removal rate was calculated. The results are shown in Table 1;

[0042]

[0043] In the formula, [M 2+ represents the concentration of M metal ions.

[0044] Table 1 Performance test of thiol-modified potato porous esterified starch prepared in Examples 1 to 3

[0045]

[0046] As can be seen from Table 1, the oil absorption rate of the thiol-modified potato porous esterified starch prepared in Examples 1 to 3 is ≥100%, the water absorption rate is ≥130%, the degree of esterification DS ≥ 1.25%, and the removal rate of lead, cadmium, chromium, and mercury ions all reaches more than 83%, indicating that it has good water absorption, oil absorption, and stability as well as good heavy metal adsorption performance.

Claims

1. A preparation method of a thiol-modified porous esterified potato starch, characterized in that, It includes the following steps: Step 1: Mix potato starch with a sulfuric acid solution with a concentration of 0.5 - 1.5 mol / L according to a mass ratio of 1:(90 - 95). Under the water bath condition of 60 - 70 °C, heat and stir for 8 - 10 min, then perform ultrasonic dispersion. After cooling, centrifuge to separate the precipitate, and freeze-dry to obtain porous potato starch. Step 2: First, add the porous potato starch into deionized water to prepare a starch milk with a mass fraction of 20% - 30%. Adjust the pH value of the starch milk to alkaline. Then, take a thiol compound and add it to the starch milk according to the mass ratio of the thiol compound to the porous potato starch of (1 - 1.5):

1. Stir at 30 - 50 °C for 3 - 8 h to obtain an esterified starch milk. Adjust the pH value of the esterified starch milk to neutral, then centrifuge to separate the precipitate, and freeze-dry to obtain thiol-modified porous potato esterified starch.

2. The preparation method of the mercapto-modified porous esterified potato starch according to claim 1, characterized in that, The average particle size of the potato starch in Step 1 is 35 μm, and the amylose content is 22%.

3. The preparation method of the mercapto-modified porous esterified potato starch according to claim 1, characterized in that, The ultrasonic dispersion in Step 1 is carried out at a frequency of 100 - 150 KHz for 5 - 10 min.

4. The preparation method of the mercapto-modified porous esterified potato starch according to claim 1, wherein, The centrifugation in Steps 1 and 2 is carried out at a rotation speed of 4000 - 8000 r / min for 5 - 10 min.

5. The preparation method of the mercapto-modified porous esterified potato starch according to claim 1, characterized in that, The temperature of freeze-drying in Steps 1 and 2 is -40 °C.

6. The preparation method of the mercapto-modified porous esterified potato starch according to claim 1, characterized in that, In Step 2, a NaOH solution with a concentration of 2 mol / L is used to adjust the pH value of the starch milk to 8 - 10.

7. The preparation method of the mercapto-modified porous esterified potato starch according to claim 1, wherein, In Step 2, a HCl solution with a concentration of 0.5 mol / L is used to adjust the pH value of the esterified starch milk to neutral.

8. The preparation method of the mercapto-modified porous esterified potato starch according to claim 1, characterized in that, The thiol compound in Step 2 is thioglycolic acid or mercaptopropionic acid.

9. A thiol-modified porous esterified potato starch prepared by the method according to any one of claims 1 to 8, characterized in that, The oil absorption rate ≥ 100%, the water absorption rate ≥ 130%, and the degree of esterification DS ≥ 1.25%.

10. Application of the thiol-modified porous potato esterified starch according to claim 9 as a heavy metal ion remover.

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